Syria's army has reportedly used helicopters to battle opposition forces in at least four Damascus neighborhoods -- an escalation of the most serious fighting in the capital since the uprising against President Bashar al-Assad began 16 months ago.

July marks the third day of fighting in at least four Damascus neighborhoods. Government troops had already been using tanks and rockets in the battle on the south side of Damascus, which started over the weekend.

Opposition fighters in the Free Syrian Army announced what they called a full-scale attack operation against regime forces which they have dubbed "the Damascus volcano and earthquakes of Syria."

The operation was described as "the first strategic step toward bringing Syria into a state of complete and total civil disobedience," with "attacks on all security stations and branches in the cities and the countryside."

The armed opposition says all foreign officers on Syrian soil that are allied to the regime are "legitimate targets" -- including Lebanese Shi'ite Hizballah militia, members of Iran's Revolutionary Guard, Iraqi militants, and pro-Assad Palestinian factions.

UN Slams 'Political Obstruction'

In Geneva, the director-general of the United Nations office for the Coordination of Humanitarian Affairs -- John Ging -- indicated that the deteriorating situation in Syria is making it difficult to deliver humanitarian aid to suffering civilians.

"We face tremendous political obstruction from the government of Syria," he said. "We face an incredibly dangerous operational environment because of the conflict itself and we face capacity issues among the organizations who are trying to scale up physically from no humanitarian, or very little humanitarian operations to a massive humanitarian operation."

According to Adrian Edwards, a spokesman for the United Nations High Commissioner for Refugees (UNHCR), refugees are fleeing Syria at an increasing rate.

"The number of Syrian refugees registered or assisted by UNHCR in Iraq, Jordan, Lebanon, and Turkey has almost tripled since April and now stands at 112,000," he said. "Three-quarters of these are women and children. The actual number of Syrian refugees is thought to be significantly higher as many people seek to be registered only when they run out of resources."

The Turkish government said a Syrian brigadier-general and several other military officers fled with civilian refugees into Turkey overnight from Syria, raising the total number of defected Syrian generals in Turkey to 18.

Those defections came after the most senior politician in the regime to defect and flee Syria urged soldiers and other political figures in the government to defect to the opposition.

Bombings 'Orchestrated' With Al-Qaeda

Earlier, Nawaf Fares, Syria's former ambassador to Iraq, told the BBC that Assad's regime won't hesitate to use chemical weapons to try to stay in power. He said unconfirmed reports indicate chemical weapons already may have been used by the regime against civilians in Homs.

Fares also elaborated on earlier allegations he made that Assad's regime and Al-Qaeda are collaborating to orchestrate major bombings across Syria.

But Fares says Al-Qaeda and Assad's regime have put aside their differences to pursue "common interests." He said Al-Qaeda is "searching for space to move and a means of support" while Assad's regime is "looking for ways to terrorize the Syrian people."

In Moscow, meanwhile, international envoy Kofi Annan was meeting with the Russian leadership on July 17 for talks on a proposed new United Nations Security Council resolution on the Syrian crisis.